There are two classes of tetrafluoroethylene polymers, non-melt-processible and melt-processible. The non-melt-processible ones are composed essentially of recurring tetrafluoroethylene units, i.e., they are substantially homopolymers of high molecular weight. They can be processed into shaped articles only by sintering or ram-extrusion, or by paste extrusion, depending on type.
In sharp contrast, melt-processible tetrafluoroethylene polymers can be melted and extruded in ordinary melt-extrusion equipment. They contain comonomer units which permit lowering the melt viscosity of the polymer enough to make the polymer melt-extrudable. Thus they can be molded into extruded articles, injection molded articles, or used as coatings for wire and tubes, and the like. The copolymers tend to undergo melt fracture as extrusion rates, i.e., speeds, increase and this results in rough surfaces of extruded articles. An increase in extrusion rates before onset of melt fracture is a desirable goal for improving these melt-processible polymers. Such an improvement is found in the copolymers of this invention.